Lubricating oils containing an antioxidant mixture of zinc and antimony dialkyl dithiocarbamates



United States Patent I 3,462,367 LUBRICATING OILS CONTAINING AN ANTIOXX- DANT MIXTURE OF ZINC AND ANTIMONY DI- ALKYL DITHIOCARBAMATES Russell L. Booher, Edwardsville, 15L, assignor to Shell Oil 1 Company, New York, N.Y., a corporation of Delaware Ne Drawing. Filed Oct. 31, 1966, Ser. No. 590,498

' int. Cl. Cllim 1/40 Ci. 25233.2 8 Claims ABSTRACT OF THE DISCLOSURE i This invention-relates to improved lubricating compositions, and more particularly to lubricating compositions which exhibit increased oxidation stability even when the compositions contain relatively large amounts of prooxidant additives.

At one time straight mineral oils were able tomeet all normal lubrication requirements of automotive and industrial practice. As these requirements became more severe with the progressive development of engines and machinery, it became necessary firstly to improve the quality of lubricating oils by new methods of refining and eventually to use additives to either reinforce existing qualities or to confer additional properties. These additives, e.g., dispersant polymers, pour depressants, viscosity index improvers, anti-wear and anti-rust inhibitors,

etc., some of which contain metals, When added in large amounts to lubricating oil, act as catalysts or accelerators in promoting oxidation of the oil. These additives may appropriately be referred to as pro-oxidant additives.

To further complicate the oxidation stability problem of lubricating oils, many of the oils are derived from crudes containing compounds which are readily attacked by oxygen, e.g., aromatics and olefins. Oil oxidation results in deterioration of the oil and formation of sludge deposits. Sludge is used to identify all types of engine deposits ranging from varnish-like films to baked carbon accumulations. Sludge causes engine wear, loss of lubricating properties of the oil and generally loss of overall engine efficiency. In the past, therefore, it has been necessary to establish a proper balance between oxidation inhibitor and, for example, detergent or dispersant in order to secure optimum oxidation resistance of the oil.

' It has now been discovered in accordance with the present invention that lubricating oil compositions containing a minor amount of zinc N,N-dialkyl dithiocarbamate and a minor amount of antimony N,N-dialkyl dithiocarbamate in solution therewith are inhibited against oxidation even in the presence of pro-oxidant materials.

According to the present invention, the carbamates which are incorporated into oil compositions are of the R S I wherein R is an alkyl radical having from 1 to carbon atoms, preferably from 4 to 6 carbon atoms; Z is either antimony or zinc; and n is an integer corresponding to the valence of Z. Both Rs attached to the nitrogen atom may be the same or different, branched or straightchained, e.g., wherein R is an ethyl, isobutyl, n-butyl, n amyl, n hexyl, heptyl radical, and the like. Preferred compounds of the above formula include antimony and zinc N,N-dibutyl dithiocar-bamates, antimony and zinc N,N-diamyl, N,N-dihexyl dithiocarbamates, and antimony and zinc N,N-dioctyl dithiocarbamates.

Base oils to which the zinc and antimony N,N-dialkyl dithiocarbamates described herein are added may be selected from a variety of natural oils such as paraffinic, naphthenic, and mixed base mineral oils having a viscosity range, e.g., from 30 SUS up to 250 SUS and higher at F. Moreover, the oils may result from crudes which have or have not been highly refined. In addition to mineral lubricating oils, the carbamates may be added to synthetic lubricating oils such as polymerized olefins, silicone polymers, esters and ethers. Mixtures of natural and synthetic oils can also be employed.

Mineral lubricating oils which are particularly desirable for use in compositions of this invention are obtained from West Texas Ellenburger crudes, East Texas crudes, Oklahoma crudes, California crudes. Useful refined oils therefrom include oils which have properties within the following ranges:

Gravity, API min 26.5 Pour point, F. max 10 Flash, COC, "F. min 390 Viscosity, SUS at 100 F 160 Viscosity index min 95 Other oils, which include a SAE 30 mineral oil, have the following property ranges:

Gravity, API min 24.5 Pour point, F. "max" 5 Flash, COC, F. min 415 Viscosity, SUS at 210 F. 58-63 Viscosity index 50-60 The dithiocarbamate combination is particularly suitable for lubricating oil compositions which contain large amounts of pro-oxidant additives or compositions which are less susceptible to inhibitors such as low viscosity oils prepared from crudes which are not highly refined. Thus, by using the combination of carbamates described herein, it is possible to formulate oil compositions which can contain relatively large amounts (up to 10% or higher) of numerous other additives such as corrosion inhibitors, pour point depressants, wear and corrosion inhibitors, viscosity index improvers, anti-foaming agents, blooming agents, detergents, and the like and yet have a lubricating life equal to or greater than present lubricating compositions which contain only moderate amounts of these additives. The lubricating life of an oil is that period of time in which the oil is an effective lubricant for its intended purpose.

Specific examples of the pro-oxidant materials include (1) nitrogen-containing polymeric additives such as the copolymers of lauryl methacrylate and N-vinyl pyrrolidone; copolymers of lauryl methacrylate, stearyl methacrylate and 2-methyl-5-vinyl pyridine; an amide-imide of a mono C polymeric hydrocarbyl succinic anhydride, and the like, (2) basic additives such as, calcium salts of high molecular weight sulfonic acids, e.g., calcium naphtha sulfonates which are treated with calcium hydroxide to form the basic salts, and the carbonated calcium sulfonates, and (3) metal ions and acid-forming materials, as well as unsaturated organic compounds, but are not limited to these materials.

The amount of additive combination incorporated into the lubricating oil compositions may var over a wide range, i.e., 0.01% to 20%, depending upon pro-oxidant materials present as well a the conditions under which the compositions are used. Ordinarily, the amount of additive combination present will be from 0.01% to 10% by weight based upon the weight of the base oil, and preferably from about 0.1% to about 5%. Preferably, the zinc and antimony dialkyl dithiocarbamates are present in weight ratios of from 9:1 to 1:9, and most preferably from 75:25 to 25275. Usually the carbamates are present in equal weight ratios. However, beneficial coaction between the carbamates is obtained even when one of the carbamates is present in only trace amounts, although to a lesser degree.

The following examples are for purposes of illustrating the invention and are not intended to limit the invention to the particular compounds and compositions described. Unless otherwise specified, percent by wt. has reference to percent by weight based-upon the weight of the base stock. In illustrating the invention, the following base stocks, compounds and compositions are referred to.

BASE STOCKS to 85 or higher.

A base oil having the following properties:

viscosity index corresponding Gravity, API 30.4 Color, AS'IM 0.;' Pour point, F. 70 Flash, COC F. 300 Viscosity SUS at F.

LVI has reference to low viscosity index corresponding to less than 40. p

A solvent refined 1'50 SUS at 100 1 neutral oil.

Compounds Compound a Zinc diamyl dithiocarbamate. Compound 11 Antimony diamyl dithiocarbamate. Compound 0 Zinc di-n-butyl dithiocarbamate. Compound d Antimony di-n-butyl dithiocarbamate. Compound 2 Zinc di-n-hexyl dithiocarbamate. Compound 1 Antimony di-n-hexyl dithiocarbamate.

The following compositions are prepared from the above base stocks and compounds.

Base stock A Composition 1: Percent by wt.

Compound (I 0.5 Composition II:

Compound b 0.5 Composition III:

Compound b 1.0 Composition IV:

Compound a 0.5

Compound b 0.5

Base stock B Composition V:

Compound a 0.5 Composition VI:

Compound b 0.5 Composition VII:

Compound a 0.5

Compound I) 0.5

In order to illustrate the effectiveness of the carbamate combination to impart unexpected oxidation stability to lubricating oils, air oxidation tests were conducted. In these tests, a stream of air (30 mL/min.) was bubbled through a 20-gram sample of lubricant (oil composition) in the presence of 20 ppm. each of copper and iron (as octoates) catalysts. The induction period, which is the length of time elapsed before a substantial increase in the rate of oxygen-uptake occurs, is a standard measure of oxidation stability and is tabulated below for each lubricant. In some instances the blotter spot life is also recorded. In the blotter spot life test, a drop of lubricant is placed on a blotter at regular intervals and a spot is formed; the time required for undispersed insolubles to appear in the spot is recorded.

These air oxidation tests were developed to simulate engine operating conditions under which sludge forms. The tests were conducted at 350 F.

OXIDATION TEST RESULTS Induction period, Blotter spoltl; lite,

Composition VII The above test results illustrate the effectiveness of the combination of a zinc dialkyl dithiocarbamate and antimony dialkyl dithiocarbamate to impart oxidation stability to oils, and particularly to oils containing pro-oxidant materials (Compositions V-VII), wherea any of the individual carbamates per se is relatively ineifective. By reason of this effectiveness, it is possible to reduce the concentration of oxidation inhibitor presently required in lubricating formulations on the one hand or to improve other properties of the formulations on the other hand by maintaining the present oxidation inhibitor concentration while increasing the concentration of pro-oxidant additives.

Other additives may also be incorporated into the lubricating compositions according to the invention, for ex ample, anti-foam agents, viscosity index improvers, rust inhibitors, and the like, as well as other anti-oxidants. As demonstrated by the tests (in particular Compositions VVII), the inhibitor combination i effective even in the presence of pro-oxidant additives.

Moreover, particularly favorable results are obtained when phenyl-alpha-naphthylamine is added to the compositions of the present invention. In an air oxidation test carried out under exactly the same conditions as those employed in testing Compositions I-VII, it wa found that when 0.2% phenyl-alpha-naphthylamine was added to Composition VII, the induction period was increased to 20 hours and the blotter spot life to 22 hours.

Compositions of this invention can be used as engine lubricants, hydraulic fluids, industrial lubricants, and the like.

I claim a my invention:

1. A lubricating oil composition comprising a major amount of lubricating oil and from 0.01% to about 10% each based upon the weight of the lubricating oil of (1) zinc di-C -alkyl dithiocarbamate and (2) antimony di- C -alkyl dithiocarbamate.

2. A lubricating oil composition comprising a major amount of lubricating oil, a minor amount of a prooxidant material, selected from the group consisting of copolymers of lauryl methacrylate and N-vinyl pyrrolidone, copolymers of lauryl methacrylate, stearyl methacrylate and 2-methyl-5-vinyl pyridine, an imide of mono C polymeric hydrocarbyl succinic anhydride, a calcium salt of a high molecular weight sulfonic acid and mixtures thereof and from 0.01% to about 10% each by weight based upon the weight of the lubricating oil of (1) zinc di-C -alkyl dithiocarbamate and (2) antimony di- C -alkyl dithiocarbamate.

3. A composition according to claim 2 wherein the pro-oxidant material includes a lauryl methacrylate/N- vinyl pyrrolidone copolymer.

4. A composition according to claim 2 wherein the pro-oxidant material include a basic calcium salt of a high molecular weight sulfonic acid.

5. A composition according to claim 2 wherein the pro-oxidant material includes a compound selected from the group consisting of a basic calcium salt of a high molecular Weight sulfonic acid, a lauryl methacrylate/N- vinyl pyrrolidone polymer and a combination thereof.

6. A composition according to claim 5 wherein the oil is a mineral oil.

7. A composition according to claim 6 wherein the dithiocarbamates are Zinc diamyl dithiocarbamate and antimony diamyl dithiocarbamate.

8. A composition according to claim 7 which contains from 0.01% to about 10% by weight of phenyl-alphanaphthylamine.

References Cited UNITED STATES PATENTS PATRICK P. GARVIN, Primary Examiner W. CANNON, Assistant Examiner US. Cl. X.R. 252-336, 42.7 

